This invention relates to telecommunications and, more specifically, to a telephone ring signal detector, detecting a telephone ring signal voltage on a telecommunications line and providing a telephone answering function on the line, prior to a first quarter cycle time period of a first telephone ring signal cycle time period.
Many premises, such as a home or a small business office, are equipped with a single subscriber telecommunication line (or a telephone line), due to cost and other considerations. Such premises often employ multiple extension telephones, which are typically connected in parallel to the telephone line and are usually located throughout the premise.
During an incoming telephone call, each premise telephone, or line telephone, detects a telephone ring signal voltage on the telephone line. Each telephone can respond to the ring signal voltage, by activating an audible telephone ringer mechanism. This "ringing" of multiple telephones throughout the premise can disturb most premise personnel until the call is answered.
Several methods have been developed to eliminate this disturbance at the premise due to "ringing" telephones. One method physically disconnects the telephones from the line, which is similar to another method that allows the user to switch "off" the audible telephone ringer mechanism. Both methods are not practical for multiple extension telephones which are widely separated throughout the premise. In addition, these methods impose a severe limitation on a telephone's usefulness, especially for incoming emergency calls. Another method utilizes a telephone answering device (TAD) connected in series between the telephone line and each telephone. During the telephone ring signal voltage, the TADs provide a non-conductive "open" circuit to the attached telephones, thereby preventing the ring signal voltage from "ringing" these telephones. One example uses a master telephone answering device (MTAD), which is the only device connected to the line. The MTAD silently answers the telephone call and switches the line to the appropriate telephone based on a caller line signal, including a "touch tone" signal and a facsimile (or FAX) signal. External telephone wiring is required between the MTAD and all extension telephones. This can be impractical for widely separated telephones located in different rooms or on different floors. Another example also utilizes a line connected MTAD, but further employs an extension telephone answering device (ETAD) connected in series between each extension telephone and the line. The MTAD silently answers the call, since the ETADs provide a non-conductive "open" circuit to the attached extension telephones. When the caller selects one of the ETADs using one of the caller line signals, the selected extension telephone is connected to the line. This method is complex and not cost effective, since each extension telephone requires an attached ETAD, and each selected ETAD must provide additional complex functions for the extension telephones to function normally.
A telephone ring signal detector can also be used to prevent the "ringing" of line telephones, by detecting a first telephone ring signal voltage and connecting a telephone device off-hook terminal impedance to the line, during the first telephone ring signal cycle time period of the first telephone ring signal. The telephone device off-hook terminal impedance is a telephone device terminal impedance when a telephone device receiver is removed from a telephone device cradle and hook switch. (A telephone device on-hook terminal impedance is the telephone device terminal impedance when the telephone device receiver is placed on the telephone device cradle and hook switch.) A Telephone Company Central Office (CO) detects the off-hook terminal impedance on the line and terminates the first telephone ring signal voltage. This prevents the first ring signal voltage from achieving sufficient magnitude or energy to activate any of the audible telephone ringer mechanisms coupled to the line. A ring signal detector, described in U.S. Pat. No. 5,544,241 to Dibner, Aug. 6, 1996, generates a ring signal detect output signal and couples the off-hook terminal impedance to the line, after a predetermined time delay from an initial time when the telephone ring signal voltage exceeds a predetermined ring signal threshold voltage. The ring detect output signal occurs anytime during the first telephone ring signal cycle time period dependent on the time delay. If the time delay is implemented by a digital timing technique to measure a time interval, then a clock, a clock cycle counter, a timing reference and a timing comparator are required as describe by Dibner. If the time delay employs an analog timing technique to measure the time interval, an energy storage element, a charging and discharge circuit, a analog reference element and an analog comparator is required. Either timing technique to measure time intervals adds cost and complexity to Dibner's ring signal detector. Dibner's ring signal detector also monitors for an inactive line, by detecting a dial tone signal, which adds further cost and complexity to the detector.